The present invention relates to an electrical machine, particularly an electrical machine for driving a motor vehicle.
With larger electrical machines, which are used, for example, for driving a motor vehicle, a cooling of the stator housing is sometimes necessary to dissipate the resulting power loss.
The object of the present invention is to specify an electrical machine which can be effectively cooled while being economic to produce and requiring little maintenance in operation.
This object is achieved by the characteristics of claim 1. The dependent claims relate to preferred embodiments of the invention.
The object is achieved by an electrical machine, particularly for driving a motor vehicle, comprising a rotor having a rotor shaft extending in the axial direction. Furthermore, a stator encompassing the rotor and a stator housing which accommodates the stator are provided. A cooling duct is integrated in this stator housing. The cooling duct is made up of a sequence of channels and deflector portions. A deflector portion is located between adjacent channels in each case. As a result, the cooling duct is formed in a meandering fashion along the circumference of the stator housing. The cooling duct in the stator housing is preferably produced by appropriate recesses during the casting of the stator housing. Alternatively or in addition, the channels and deflector portions of the cooling duct can also be produced by machining. The invention enables the cooling duct to nestle very closely against the radii to be cooled. Furthermore, the stator is very easy to construct, wherein the cooling duct can be integrated at the same time. For example, a multi-layer structure of the stator housing is not necessary to form the cooling duct; however, this is not excluded.
The directions on the electrical machine are defined as follows: The rotor shaft extends in an axial direction. Perpendicular to the axial direction is a radial direction. A circumferential direction is defined perpendicular to the radial direction and perpendicular to the axial direction. Accordingly, a sleeve surface of the stator housing extends along the circumferential direction. The two face sides of the stator housing lie perpendicular to the axial direction and parallel to the radial direction.
Preferably, it is provided that the channels and deflector portions merge impermeably into one another, thus forming a closed cooling duct. As a result, the coolant, in particular a fluid coolant, can only flow along pre-defined paths through the cooling duct. In particular, the coolant flows from one channel via a deflector portion into the next channel, and from this channel in turn via a further deflector portion into the next channel. The individual channels therefore each have only two openings, next to which a deflector portion is arranged in each case. Furthermore, it is preferably provided that a deflector portion connects only two channels to one another. This specifies a defined path for the coolant in the cooling duct. Alternatively, however, a deflector portion can also combine the coolant flow from two or more channels and/or distribute it between two or more channels in any proportion.
In a preferred embodiment, the channels are rectangular. Furthermore, preferably, a channel width is defined in the circumferential direction and a channel height is defined in the radial direction. Particularly preferably, it is provided that a ratio of channel height to channel width lies between 1/10 and ½. As a result, relatively wide channels with relatively low height are provided. This results in a low thickness of the stator housing in the radial direction and, at the same time, enables the surface area for transferring heat between the coolant and the stator to be cooled or the stator housing to be cooled to be very wide.
Advantageously, the channels in the sleeve surface of the stator housing extend parallel to the axial direction. With an arrangement of the channels parallel to the axial direction, the deflector portions enable a deflection through approximately 180 degrees. Preferably, however, a deviation from the axial direction by up to thirty degrees is also possible. An arrangement of the channels in the motor housing in parallel open rings around the motor axis is also conceivable, wherein the individual rings are in each case connected to one another by deflector regions.
The deflector portions are designed in such a way that the coolant can be rerouted from one channel to another channel very effectively. In doing so, attention must be paid to the flow of the coolant in order to reduce the energy expended for a coolant pump. Furthermore, as few dead water zones as possible must form in the coolant flow, so that the coolant is always in motion and is able to dissipate as much heat as possible.
Preferably, it s therefore provided that a ratio of the maximum cross-sectional area in the deflector portion to the mean cross-sectional area in the channel lies between 0.5 and 4. Preferably, this ratio lies between 1 and 2.
In an advantageous embodiment, the deflector portions extend in the circumferential direction and the channels open out laterally into the deflector portions.
For this purpose, the deflector portions are formed, for example, from straight tubes. These tubes extend in the circumferential direction and the channels open out into the sleeve surface of the tubes. The cross section of the tubes is in particular rectangular or round. The tubes can be straight or slightly curved. The slightly curved tubes provide a very loss-optimized flow deflection from one channel to another channel.
Particularly preferably, the deflector portion is banana-shaped. If this banana shape is viewed along the circumferential direction, then the cross-sectional area in the deflector portion initially increases up to a maximum value. From this maximum value, the cross-sectional area in the deflector portion decreases once more. The two channels open out laterally into the sleeve surface of this banana shape.
In particular, it is provided that the banana-shaped deflector portion has a convex curvature. The convex curvature extends in the axial direction and/or in the radial direction. In particular, the curved form of the banana is defined as follows: The banana shape is bounded on the axial side by a wall. This wall is curved in the axial direction and therefore has a “convex curvature in the axial direction”. The banana shape is likewise bounded outwards or inwards, that is to say outwards or inwards in the radial direction, and can be curved. Here, the banana-shaped deflector portion has a convex curvature in the radial direction.
In a preferred embodiment, a radially innermost boundary of the channels is at the same distance from the rotor shaft as a radially innermost boundary of the deflector portions. In particular, this design is preferably provided in conjunction with the banana-shaped deflector portions. The curvature of the banana-shaped deflector portion therefore extends exclusively outwards in the radial direction. On the one hand, this results in a flow-optimized deflection routing for the cooling medium. On the other, this design enables a very large surface area to be formed between the stator and the cooling duct.
In a further alternative, the deflector portion is in the form of a sharply curved tube. Here, the tube is curved to the extent that the channels can open out into the tube on the face side. In the case of channels which are arranged in parallel, this means that the tube is curved through 180 degrees. This curved tube can have a round, oval or rectangular cross section.
The rotor shaft is preferably mounted in the stator housing. The cooling duct can therefore also be used simultaneously for cooling the bearing of the rotor shaft. Particularly preferably, the cooling duct has a bearing cooling loop instead of a deflector portion at least one point. The bearing cooling loop leads from the end of one channel, preferably around the bearing of the rotor shaft, to another channel.
Alternatively, it is also possible to relocate the deflector portions in the face side of the stator housing in order to form the bearing cooling loop. As a result, the deflector portions are closer to the bearing and can be used better for cooling the bearing. In particular, at their ends, the channels have intermediate pieces curved through approximately 90 degrees for this purpose. These intermediate pieces are curved in the direction of the rotor shaft, so that the deflector portions are then arranged in the face side of the stator housing.
The deflector portions in the overall cooling duct do not all have to have the same design. It is therefore also provided that different deflector portions are arranged between the channels. It is equally possible to form a bearing cooling system for the bearing of the rotor shaft on only one side or on both sides. The bearing cooling system can be different on both face sides; for example, a bearing cooling loop can be formed on one face side and the deflector portions can be relocated in the face side of the stator housing for cooling the bearing on the other face side.
Furthermore, it is preferably provided that the stator housing comprises a base body and a cover. The cover substantially forms the one face side of the stator housing. The deflector portions of one axial side and the channels are preferably formed in the base body. The deflector portions of the other axial side are then located in the cover. The two-part design of the stator housing results in easier production of the hollow spaces. A design with a sleeve element and two face-side covers is likewise conceivable.
Preferably, the cooling duct includes at least two connections for a coolant pump.
Preferably, the electrical machine is used for driving a motor vehicle.
Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawing. In the drawing:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.